The present invention disclosed herein relates to a photonics device, and more particularly, to an electro-optic modulating device.
Silicon photonics technologies, which are alternative technologies for solving serious heat generation in computing devices and bottlenecks in data communication between semiconductor chips, are becoming an increasingly important issue. The silicon photonics technologies have been significantly developed for the past few years. Examples of the silicon photonics technologies include fast silicon optical modulators, Si—Ge photo-detectors, silicon Raman lasers, silicon optical amplifiers, silicon wavelength converters, and hybrid silicon lasers. Nevertheless, the last data transmission rate that has been realized by silicon modulators is about 10 Gb/s so far. Much faster modulation and data transmission characteristics need to be implemented to meet an increase of a bandwidth that is required for next-generation communication networks and future high-performance computing devices.
Most commercialized high-speed optical modulators are based on electro-optic materials such as lithium niobate and group III-V semiconductors, and are known to provide modulation characteristics of about 40 Gb/s (much faster than 10 Gb/s). In contrast, since single crystal silicon is a material without linear electro-optical characteristics (i.e., Pockels effect) and takes very weak Franz-Keldysh effect, it is difficult to implement fast modulation characteristics in silicon.
Although strained silicon was known to take the Pockels effect in recent years, its measured electro-optic coefficient is much smaller than that of LiNbO3. Also, even though strained Ge/SiGe quantum well structures was known to have relatively high electro-optic absorption characteristics because of the Quantum Confined Stark Effect, various technical limitations (e.g., strain engineering) must be solved in order to implement the strained Ge/SiGe quantum well structures.
As known so far, the high-speed modulation in silicon may be implemented only through the free carrier plasma dispersion effect. In silicon, a variation of the free carrier density incurs a variation of the refractive index of material, and thus the modulation rate of a silicon modulator based on the free carrier plasma dispersion effect is determined by how quickly the free carriers can be injected or removed. Device configuration proposed to implement phase modulation in silicon is roughly divided into three types of forward biased p-i-n diodes, MOS capacitors, and reverse biased PN-junctions.
The forward biased p-i-n diode manner disclosed in U.S. Pat. No. 5,908,305 has been proven to provide high modulation efficiency. However, because of slow charge generation process and slow recombination process, the forward biased p-i-n diode manner has a limitation in the modulation rate unless the lifespan of charges is dramatically reduced.
Both of the MOS capacitor and the reverse biased PN-junction are potentially based on the electric-field induced majority carrier dynamics that may realize about 10 Gb/s or more. However, these manners require a long phase-modulator due to low modulation efficiency. In addition, the reverse biased PN-junction manner disclosed in U.S. Pat. Pub. No. 2006/0008223 has a technical limitation in that optical waveguide loss is large because the entire region of an optical waveguide for phase-modulation is very heavily doped.